Phosphorus-containing flame-retardants are perceived to be more environmentally friendly than halogen containing flame-retardants. In the field of epoxy resins and laminates, organo-phosphorous flame-retardants with reactive groups, such as those derived from 9,10-Dihydro-9-Oxa-10-Phosphaphenantrene-10-oxide (DOPO), are commonly used in epoxy resin formulations because they react with the epoxy to form a phosphorus-modified epoxy resin. However, “additive” organophosphorus flame-retardants, which do not have reactive groups, are typically not used in epoxy formulations, since it is believed that covalent bonding between the epoxy resin and a reactive organophosphorus flame retardant are needed to provide high glass transition temperatures and dimensional stability.
DOPO-derived additive compounds, useful as flame-retardants, have been produced by reacting DOPO with halogen-containing compounds (see Japanese Kokai Patent Application No. Hei 11 [1999]-106619 and Japanese Kokai Patent Application No. P2001-270993A). However, DOPO-derived compounds have not heretofore been produced by reacting DOPO with dial compounds in the presence of a catalyst.